The present invention relates generally to methods for reducing residual contaminants in high density plasma chemical vapor deposition (HDP-CVD) processes and more particularly, to a method to quickly and effectively remove residual fluorine contamination present in HDP-CVD processing chambers.
As devices become smaller and integration density increases, the high density plasma chemical vapor deposition (HDP-CVD) process has become a key process due to its gap-filling capability. In many cases it is advantageous to process both flourine-doped silicate glass (FSG) and undoped silicate glass (USG) in the same HDP-CVD machine. Undesirably, after processing FSG, residual fluorine remains, making it undesirable to use the same HDP-CVD machine in a subsequent USG process without a cleaning procedure. The high density and low pressures inherent in HDP-CVD processes increases sputtering on the process chamber interior surfaces. As a result, conventional techniques such as providing passivation layers for controlling the contaminant levels have proven to be ineffective in reducing contaminants to acceptable levels in high-density plasma environments.
The residual fluorine remaining in the HDP-CVD chamber can contaminate subsequent processing steps such as USG as well as alter important processing parameters thereby detrimentally affecting subsequent processing. For example, the depositionxe2x80x94sputtering rate ratio (D/S ratio) will undesirably decrease as a result of residual fluorine contamination. The D/S ratio is a commonly used measure of the gap-filling capability of the process. Among the disadvantages of a lower D/S ratio include the possibility of xe2x80x9ccorner clippingxe2x80x9d or xe2x80x9cedge erosionxe2x80x9d along the edges of metal lines and the lowering of processing throughput since it requires a relatively longer period of time to achieve the formation of the HDP-CVD oxide.
One solution to the problem of fluorine contamination in HDP-CVD processes has been to subject the HDP-CVD chamber to a wet chemical cleaning process, requiring machine shut-down thereby resulting in a loss of valuable HDP-CVD apparatus up time.
There is, therefore, a needed solution and a method whereby both fluorine contamination and HDP-CVD apparatus down time is minimized, allowing for example, a more efficient shift in use of the HDP-CVD apparatus from FSG processing to USG processing.
It is therefore an object of the invention to provide a method whereby both fluorine contamination and HDP-CVD apparatus down time is minimized, allowing for example, a more efficient shift in use of the HDP-CVD apparatus from FSG processing to USG processing.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a method for removing residual fluorine in a HDP-CVD chamber.
According to one embodiment of the present invention, a method is provided for removing residual fluorine in a HDP-CVD chamber which includes forming a high density plasma in the presence of at least a microwave power, a silicon source, and an oxygen source whereby a silicon-rich oxide film is deposited over at least part of the inner surface of the HDP-CVD chamber; supplying a process gas comprising NF3 in the presence of microwave power to form a plasma thereby removing fluorine from the silicon-rich oxide film into the gas phase; and, removing fluorine-containing gas from the HDP-CVD chamber.
In related embodiments, the silicon-rich oxide film comprises pores ranging from about 30 per cent by volume to about 90 percent by volume. Further, the silicon-rich oxide film is deposited at a pressure such that the silicon-rich oxide film is deposited substantially over an upper portion of the HDP-CVD chamber. Further yet, the silicon source includes silane and the oxygen source includes oxygen.
In another aspect according to the present invention, the method according to the present invention further includes supplying a control wafer to the HDP-CVD chamber; and, depositing a silicon-rich oxide film over the control wafer;
In another aspect of the present invention, the method according to the present invention further includes repeating at least one of the steps until fluorine present in the silicon-rich oxide film deposited over the control wafer reaches a pre-determined level.
In another embodiment, a method of removing residual fluorine in a HDP-CVD chamber which includes forming a high density plasma in the presence of at least microwave power, a silicon source, and an oxygen source whereby a first silicon-rich oxide film is deposited over at least a part of the inner surface of the HDP-CVD chamber; supplying a process gas comprising NF3 in the presence of a microwave power to form a plasma thereby removing fluorine from the first silicon-rich oxide film into the gas phase; removing fluorine-containing gas from the HDP-CVD chamber; positioning a control wafer to the HDP-CVD chamber; and, depositing a second silicon-rich oxide film over the control wafer.
These and other embodiments, aspects, advantages and features of the invention will become better understood from a detailed description of the preferred embodiments of the invention which are described in conjunction with the accompanying drawings.